Despite taking his third pole position in a row, the German is keeping his optimism in check ahead of Sunday's race, citing his car's tyre-chewing performance in Spain two weeks ago as a genuine concern.
"I'm happy to be starting first, [but] in Barcelona we were struggling a lot in the race, [finishing] 70 seconds behind the race winner.
"We are improving, but it is difficult to understand the tyres and get the most out of them. We're improving step-by-step, but there are still a lot of questions marks remaining.
"It will be difficult tomorrow, it is our weakness. Hopefully better than Barcelona, but it is still a weakness. It could also be a bit better than expected - let's wait and see."
Rosberg added that the start will be key, and that getting through the first corner in the lead is a must.
"The start will be important, to get to the first corner first," he said.
"I have the advantage as I am first, after that we have to see how it goes, who is quickest with strategy."
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